Visual input to the hypothalamus synapses mainly in the suprachiasmatic nucleus (SChN), which therefore must be important in the many light-influenced behavioral and physiological functions of the body not connected to the classical optic pathways. The mechanisms by which the SChN accomplishes its functions (e.g., timing ability; influences over behavior and endocrine glands) are unknown. As a first step towards understanding how the SChN operates and in order to learn more about the functions of the SChN, I propose to study its neural connections using the horseradish peroxidase (HRP) tracer technique. By following retrogradely and anterogradely transported HRP by light and electron microscopy, neurons, fibers, and synapses will be functionally identified. During the course of pilot studies for this project, a modified technique for enhanced anterograde transport of HRP was discovered which will be further developed and used in this study.